What is an Oxygen sensor & do I need one?

What is an O2 sensor?

There is a little bit of confusion in regards to the O2 sensor, including what it is and what it does. 

The oxygen sensor is an electronic device used to measure the amount of oxygen in a gas or liquid.  It was developed in the late 1960’s and is most commonly used to measure the concentration of oxygen in exhaust gasses, to allow the adjustment of the air-fuel ratio so that a car’s engine can work at its optimal fuel efficiency level.  Interestingly, divers also use a very similar apparatus to measure the pressure of oxygen in their breathing gas.

Where is the O2 sensor found?

Most newer vehicles have two sensors, one on the exhaust pipe, close to the engine and another close to the muffler and catalytic converter.  Having two O2 sensors means that the vehicle has two readings provided to the engine computer, so that the vehicle can fine tune it’s performance.

Do you know what type of vehicle has four sensors?  (you’ll find the answer at the bottom)

What does the O2 sensor do?

The O2 sensors in your car monitor the amount of oxygen in your exhaust system to confirm that the vehicle is running efficiently and that the catalytic converter is functioning properly.  The sensor determines whether the engine air/fuel mixture is too rich (too much fuel) or too lean (not enough fuel) by burning a portion of the oxygen as it travels through the exhaust system.  The reading is turned into an electrical signal which is dispatched to the engine control computer.  The computer adjusts the vehicle fuel metering and timing to maintain an optimum mixture.

O2 sensors are mainly used in a “closed loop” scenario on modern cars. This refers to when a car is either idling or just cruising at a certain speed and performance is not the primary goal (e.g. highway driving).

How long do O2 sensors usually last?

The sensors in older vehicles had a much shorter lifespan than modern cars. If your car was built before 1996, your sensors may last about 90,000 kms.  Cars built after 1996 have O2 sensors which can easily last as long as 160,000 kms. A great time to have your O2 sensor inspected and replaced is during a logbook service.

What happens when the sensor is malfunctioning?

The only way to know for certain if your sensor is malfunctioning is using a diagnostic code reader.  There are some items which often point to this issue, such as:

  • Fuel usage increasing without a change of driving habits
  • Reduction in car performance
  • Engine running rough which doesn’t improve after replacing spark plugs
  • Engine light on the dashboard notifying the driver of an issue found by the engine computer. To learn more about different types of dashboard lights, read our article titled Common Dashboard Warnings Explained.

Why does a sensor fail?

Some of the reasons sensors fail include:

  • Fuel that is contaminated
  • Carbon deposits on the sensor from an engine that has started to burn oil
  • Sensor has reached its end of life

If you believe that your O2 sensor is failing or you would simply like to have it checked by a professional, book an appointment with the friendly service team at Australian Mechanical.

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